Expt 4 chemical equilibium PDF

Preview

Summary

lab report...

Description

CHEMISTRY 110

NAME

EXPERIMENT 4

SECTION

CHEMICAL EQUILIBRIUM: EQUILIBRIUM INVESTIGATIONS

DATE

AND LE CHÂTELIER’S PRINCIPLE

INSTRUCTOR

OBJECTIVES: This experiment will examine such shifts in equilibrium when changes in concentration or temperature of the system (Le Châtelier’s Principle).

DATA & OBSERVATIONS: Part A

Equilibrium Involving Thymol Blue Thymol blue (blue form) + H +

H- Thymol blue+ (yellow form)

Write the equations for the equilibrium system

H-Thymol blue+ (yellow form) + H+ H2- Thymol blue2+ (red form)

Table 4.1 Equilibrium of thymol blue Reagent Added

Colour Observed

Species causing stress

Direction of equilibrium shift

N/A

N/A

Initial Colour (step 1)

Blue 1M HCl (step 2)

1M NaOH (step 3)

red

H+

shift to products side ( right)

Yellow

OH-

Blue

OH-

reaction side (left)

1M NaOH (step 4)

reaction side (left)

Part B

Equilibrium Involving Thiocyanatoiron(III) Ion

Write the equation for the equilibrium system

Fe3+(aq) +SCN- (aq)

Table 4.2 Equilibrium of Thiocyanatoiron(III) Ion Colour observed when looking down the length Reagent Added of the tube Fe(NO3) 3 (step 1)

Direction of

stress

equilibrium shift

N/A

N/A

N/A

N/A

N/A

N/A

clearly

Control (tube A) (step 3) KCl (tube B) (step 5)

light amber

amber

Fe(NO3)3 (tube C) (step 6) KSCN (tube D) (step 7)

Fe 3+ and Cl- =FeCl3 Fe 3+ increase

darker red

toward product side(right)

amber

Fe 3+ and OH- produce Fe(OH)3

toward reaction side (left)

Equilibrium Involving Cobalt(II) Complexes

(aq) + 4Cl-(aq)

Equilibrium of Cobalt(II) Complexes

Reagent Added Water, to 1st beaker (step 2) 6M HCl, to 2nd beaker (step 3) Water, to 2nd beaker (step 4)

Colour Observed

Species causing stress

Direction of equilibrium shift

N/A

N/A

pink

Cl-

purple

toward product side(right)

water molecules

pink

Heat 2nd beaker (step 5)

purple

Cool 2 nd beaker (step 6)

pink

Revised Spring 2019

toward product side(right)

SCN- increase

Write the equation for the equilibrium system Table 4.3

toward reaction side(left)

darker red

NaOH, centrifuge (tube E) (step 8)

Part C

Species causing

Light yellow

KSCN (step 1)

FeSCN2+ (aq)

Heat

endothermic.

Cool ( temperature decrease）

2

toward reaction side(left) toward product side(right)

toward reaction side(left)

Chem 110 Expt. # 4 Chemical Equilibrium

Part D

Equilibrium Involving Copper(II) Complexes

Write the equation for the equilibrium system Table 4.4

[Cu(H2O)6]2+(aq) + 4NH3(aq) ⇌ [Cu(NH3)4(H2O)2)]2+(aq) 4H2O(l)

Equilibrium Involving Copper(II) Complexes

Reagent Added

Colour Observed

Initial Colour (step 1)

Blue 1M NH3 (step 2)

deep blue 1M HCl (step 3)

Blue

Species causing

Direction of

stress

equilibrium shift

N/A

N/A

NH3 molecules

toward product side(right)

H+， NH3 molecules form NH4+ ions toward reaction side(left)

TREATMENT OF DATA: For each part of the experiment, re-write the equilibrium equations that are relevant. Use Le Châtelier’s Principle to explain how each equilibrium shifts, in response to the “stresses” which were applied. Refer to the hints provided in the lab manual. Part A

Equilibrium Involving Thymol Blue

Part B

Equilibrium Involving Thiocyanatoiron(III) Ion

Part C

Equilibrium Involving Cobalt(II) Complexes

Part D

Equilibrium Involving Copper(II) Complexes

The equilibrium in Part D initially involves the formation of OH⁻ ions in NH3 solution: NH3(aq) + H2O(l) ⇄ NH4⁺(aq) + OH⁻(aq) The OH- ions then react with Cu2+(aq) to give a precipitate of Cu(OH)2. Cu2+(aq) + 2OH⁻(aq) Cu(OH)2(s) When more NH3 was added, NH3 molecules replaced H2O in Cu2+(aq): Cu(H2O)4 2+(aq) 4NH3 ⇄ Cu(NH3)4 2+(aq) + 4H2O(l) H⁺ ions can react with NH3 to give NH4⁺; therefore, the equilibrium shifts in response to this change.

QUESTIONS: 1. In Part A, how would increasing the concentration (molarity) of the NaOH solution from 0.1 M to 0.2 M affect the number of drops required for the observed colour changes?

2. If the hydrated cobalt(II) ion complex was refrigerated, what would you predict as the colour of the refrigerated solution?

3. Look at the equilibrium equation for the reaction involving the hydrated cobalt(II) ion complex.

From your lab results, is the forward reaction endothermic or exothermic? Give reasons for your answer.

4. Summarize Le Châtelier’s principle including comments on how changes in concentration of reactants, products and temperature affect a system at equilibrium....